Defining Perks
Perk are the primary way characters gain new abilities.
Obtaining Perks
Like Skill Ranks, Perks with a higher rank cost more XP to purchase. Unlike Skill Ranks, you needn't purchase Pein order. You are free to choose which Perks you obtain, provided you meet its requirements.
Requirements
Most Perks also have other requirements, such as a specific Skill Rank, a prior Perk, or knowing a spell. You must meet these requirements in order to obtain a Perk and if you fail to meet them later, you lose the benefits of that Perk until you meet them again.